The present subject of major emphasis is the characterization of insect yolk proteins (vitellins) and their precursors (vitellogenins) synthesized in the fat body, and the nature of the control of synthesis by juvenile hormone and other possible stimuli. In the African migratory locust (Locusta migratoria migratorioides), vitellogenin, a lipoglycoprotein of molecular weight 550,000, is synthesized as two precursor polypeptides of about 250,000 daltons, which dimerize as well as undergoing proteolytic cleavage within the fat body cell. Synthesis is dependent on juvenile hormone or an active analog. After treatment of a latectomized adult female locusts with the synthetic analog ZR 515, induced synthesis of DNA, RNA and vitellogenin are observed. The relationships of synthesis of DNA and different functional classes of RNA to that of the new protein are being studied. It is proposed to continue the analysis of this system, including a search for cellular receptors of the hormone and their role in the induced synthesis of new macromolecules.